Unraveling How Potassium Bound to Soil Minerals is Made Bioavailable for Uptake by Plants

The Science 

Potassium is an essential element for plant growth. However, soils generally have low amounts of potassium readily available to plants. Luckily, soils contain potassium in soil minerals, and there are many species of microbes that can weather mineral surfaces by secreting organic acids that dissolve the minerals, thereby releasing potassium. This research shows that the bonding environment of potassium in different organic acids has different signatures that can be detected using X-ray techniques. The signature of the bonding environment can inform whether potassium is associated with carbon, nitrogen, or oxygen.  

The Impact 

Results from this research, conducted by a multi-institutional group of scientists, are some of the first of their kind—identifying the particular signature of potassium organic acids. This understanding will allow future researchers to fingerprint the type of organic compound that is bonded to potassium in complicated biological and environmental samples, something that was not previously known to be possible until now. A further impact of this research is the characterization of these signatures; this will allow future studies to spatially distinguish between these potassium organic molecules in natural soil. Overall, this research is important to general understanding of how potassium is cycled between the soil matrix, microorganisms, and plants. 

Summary 

Microbial mineral weathering has been shown to be a promising pathway to sustainably increase the availability of potassium (K) to plants. However, the mechanisms underlying microbial K transformations are poorly resolved. To better understand how microbes source K from minerals, a multi-institutional team of scientists performed X-ray absorption spectroscopy (XAS) at the Stanford Synchrotron Radiation Lightsource (SSRL) on K-organic salts, including acetate, citrate, nitrate, oxalate, and tartrate, which are frequently observed as acids secreted by soil microbes. The organic salts display XAS spectra, each of which demonstrate numerous unique features. To identify the electron moves that cause some unique spectral features in the organic salts, the team used computational tools and expertise from scientists at the Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy, Office of Science user facility, and Pacific Northwest National Laboratory to simulate experimental spectra. The team analyzed the K-organic salt bonding in detail to explain why XAS spectral shapes differ. Their results also indicated that XAS spectra were associated with the entire compound, despite similar bonding environments around the K ion of each organic salt. The improved understanding of K bonding environments with organic compounds provides an important toolkit to understand how K is transformed by microbial processes and made bioavailable for plant uptake. 

Contacts 

Jocelyn Richardson, SLAC National Accelerator Laboratory, jocelynr@slac.stanford.edu  

Ritimukta Sarangi, SLAC National Accelerator Laboratory, ritis@slac.stanford.edu  

Arunima Bhattacharjee, EMSL, arunimab@pnnl.gov  

Funding 

Use of the SSRL at the SLAC National Accelerator Laboratory was supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences program. The SSRL Structural Molecular Biology Program is supported by the DOE Biological and Environmental Research program and the National Institutes of Health, National Institute of General Medical Sciences. A portion of this research was performed on an Exploratory project award from the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility, sponsored by the Biological and Environmental Research program. 

Publication 

J.A. Richardson, et al. "X-ray absorption spectroscopy and theoretical investigations of the effect of extended ligands in potassium organic matter interaction." The Journal of Chemical Physics (2024) 160, 044114. [DOI: 10.1063/5.0183603]